The present invention relates to an instrument for surgical purposes, especially for coagulation, and to a method of cleaning said instrument.
In surgery or microsurgery, coagulation has a very wide field of indication. Conventionally coagulation is caused with the aid of forceps, tweezers, a wire or a blade to stop bleeding from open wounds. For example the bleeding vessel is pressed together with the forceps or tweezers and then a high-frequency current is led through the tip (bipolar application).
The high-frequency current can also be introduced into the surrounding tissue, e.g. via a blade. In this case a large-area electrode functions as a counterelectrode; current flows through the body, coagulation takes place in the region of the blade, i.e. the region of highest current density (unipolar application).
In both cases, the electrical resistance of the tissue causes conversion of the electrical energy into thermal energy and thus the heating up and coagulation of the tissue, i.e. the clotting of the cell substance.
Tweezers or forceps for surgical purposes are known, for example, which are suitable for unipolar and bipolar coagulation and have two arms moveable towards one another and which are electrically insulated from one another. These arms have at their tips electrical contact surfaces formed from metal. These electrical contacts are connected to a control unit. When a piece of tissue is touched/grasped between the two facing inner sides and a flow of current through the contacts or the tissue is activated, there is coagulation of the grasped tissue.
These surgical instruments according to prior art have a number of disadvantages.
Often, when metals are used, this results in undesired adhesion of the tissue to the metal surface, which in the worst case can cause the coagulated part to tear away again.
Moreover, the use of conventional surgical instruments having metal contact, surfaces is expensive, since after an operation the instruments are either thrown away or have to be expensively mechanically and chemically cleaned, there always being the risk that, e.g., tissue or blood residues remain.
A particularly high risk arises from the contaminated electrodes. Dried-on blood or tissue residues are here sufficient to electrically insulate the metal contact surfaces; this can lead first to circuit failure and than to sparking or carbonization of the contact surface and burning of the tissue on the contact surface. Moreover, additional risks arise where infectious tissue adheres.
Moreover, the limited thermal conductivity of the metal used can lead to irregular heating of the metal during the coagulation process and to the formation of local temperature peaks (xe2x80x9chot spotsxe2x80x9d). There is reason to suppose that burned tissue is produced and continues to adhere at these xe2x80x9chot spotsxe2x80x9d even in normal use. This means a dangerous loss of quality in tweezers according to prior art.
The heating capacity of metals can also have a disadvantageous effect, since through the residual heat stored in metal the coagulation process is possibly continued for longer than desired by the operator, such that there is undesired xe2x80x9cinertiaxe2x80x9d of the instrument which can cause burns or adhesions, and this is very disadvantageous particularly in microsurgery.
The object underlying the present invention is, therefore, to create an instrument which overcomes the above-described disadvantages of conventional instruments, especially with respect to the production and elimination of adhesions.
This object is achieved in respect of the instrument of the present invention.
Because the contact regions consist of a diamond doped to produce electrical conductivity, the disadvantages of conventional contacts in respect of thermal conductivity, heat capacity, lacking inert properties or undesired adhesion, as well as contamination on the contact regions and difficulty of cleaning and irregular current conduction resulting therefrom are avoided. The coagulation can here occur either through direct contact of the tissue with the diamond electrode and the existing flow of current through the tissue, or through capacitive energy transmission, such as with an insulated electrode to which electricity is applied. In each case, above all, the capability of cleaning the contact regions or the instrument is greatly improved and the risk of adhesion of tissue reduced.
Diamond has the advantage that it is completely inert chemically and thus biocompatible. As a result of the physical structure, no diffusion of doping agents out of the diamond can occur. Thus, it can be used without hesitation in surgery. In addition to the inert properties of diamond at the surface of the contact region, the capacity of the diamond surface for termination (i.e. deliberate application of chemisorbed molecules or atomsxe2x80x94such as e.g. oxygen, fluorine (hydrophilic) or hydrogen (hydrophobic)xe2x80x94to the surface) renders possible the deliberate setting of the physical and chemical properties of the surface, such as its hydrophobicity/hydrophilicity. Through suitable termination of the surface, the adhesion of tissue can be further reduced or avoided.
The thermal conduction properties are also radically improved. This is due to the fact that diamond as an insulator and doped as a conductor has extraordinarily high thermal conductivity, which is even significantly higher than that of metals such as copper or silver. Thus, there is quickly uniform heat distribution within the contact region; no high temperature gradients occur which could cause the formation of a hot spot.
The thermal capacity of the diamond contact region can also be kept very low. Diamond has first of all a low specific heat capacity, which is practically independent of the doping. Moreover, diamond can be deposited in thin layers but nevertheless in a stable manner, such that a very low thermally active mass is produced.
The particular suitability of contact regions formed from highly doped diamond arises moreover from the fact that the electrical resistance of this material is largely independent of temperature. Admittedly, other semiconductor substances with a large band gap also show extensive independence of temperature in the temperature range of the application (e.g. SiC), but only diamond is simultaneously chemically inert.
A further great advantage of the diamond contact regions according to the invention arises from the fact that adhesions to the diamond which have possibly occurred anyway can be removed relatively simply. Diamond here shows good resistance to mechanical and aggressive chemical cleaning. Moreover, with the method according to the invention it is possible to clean the contacts electrolytically, without the electrode material being damaged. Thus the instrument according to the invention can be reused often and is thus economical and, environmentally friendly. Because of the possibility of reuse, in other places the instrument can also assume other high-grade embodiments which represent an improvement for the operator without any economic disadvantages arising.
The present invention has advantageous embodiments.
One advantageous embodiment provides for the contact regions to have an electrically conductive core. This core, which preferably consists of a (hard) metal or of materials often used in medicine such as niobium, iridium, tantalum, tungsten or titanium, is, on the one hand, mechanically able to bear a heavy load and on the other hand represents a good electrical conductor, which makes the connection with the contact region. The core can also consist of graphite, Zr or carbon-fibre-reinforced carbon. The deposition of diamond from a plasma leads to a chemical bond between the core material and the diamond layer. Thus very strong bonding of core-material and contact region is produced. CVD (chemical vapor deposition) methods are used here which are particularly suitable for coating three-dimensional materials. Special attention should be drawn to hot-filament CVD. This is very flexible in respect of the shape of the components to be coated (and can thus even be used for coating drills). In addition to hot-filament CVD, microwave plasma CVD and ECR-supported (electron cyclotron resonance) microwave CVD are also possible. Common advantages of these methods are good homogenous coating of three-dimensional components and high flexibility in respect of the shapes which can be coated.
However other embodiments of instruments which provide no electrically conductive core are also advantageous. Thus it is possible, for example, to produce the core of the arms of the instrument according to the invention from a material which is not electrically conductive and to coat this core over its full length, i.e. from the coagulation tip up to the connection contact for the voltage supply, with an electrically conductive layer, e.g. the doped diamond layer according to the invention. An insulating material can be applied to regions of this coating as required.
Moreover, additional embodiments of the invention are possible, for instance an electrically conductive or non-conductive diamond core. Furthermore, it is also possible to apply intermediate layers between any type of core and the doped diamond layer according to the invention. One embodiment provides for additional conductive layers to be applied at least in regions to the conductive doped diamond layer of the contact region. In this case, the diamond serves to avoid hot spots through improved heat distribution in the contact region.
An advantageous embodiment has proved to be that the concentration of doping agent in the contact region is more than 5xc3x971018 cmxe2x88x923. As particularly advantageous doping agents should be mentioned boron, sulphur, lithium or titanium; nitrogen, phosphorus or sp2-bonded carbon are also possible in the diamond layer, for example. The initially outlined advantages here arise in a special manner in that the specific resistance of the doped diamond of the contact regions is lower than 100 Ohm cm, preferably lower than 1 Ohm cm, by particular preference lower than 0.01 Ohm cm, while the average layer thickness of the contact region is up to 300 micrometers, preferably less than 10 micrometers, by particular preference 1 to 5 micrometers. With these parameters it is guaranteed that the series resistance of the coating is low, such that negligible self-heating occurs; the sensible heat is moreover quickly passed to the surroundings through the high thermal conductivity and low heat capacity.
A particularly advantageous embodiment arises from the fact that the surgical instrument can be operated with control units according to prior art (i.e. no expensive new purchase of a control unit is necessary). However, the instrument can also be electrically connected to a special control unit according to the invention, which only represents a very small modification of those of prior art (this is supplemented by a xe2x80x9ccleaning optionxe2x80x9d, i.e. a voltage source is provided which serves as a voltage supply in the following electrochemical cleaning). In any case, both control units have a high-frequency generator to generate unmodulated and modulated high-frequency currents through the contact regions.
However, it is particularly advantageous that the control unit according to the invention has an immersing basin which can be filled with liquid for dipping the contact regions into this liquid, and a voltage source to apply a d.c. or a.c. voltage to the contact regions dipped into the liquid, or can be connected to the immersing, basin/voltage source. By this means, possibly even without rough mechanical prior cleaning, the diamond contact region can be electrochemically cleaned-of adhesions. This can, depending on the choice of the other method parameters, take place so thoroughly that e. g. subsequent additional steam sterilization can possibly be dispensed with (although this is still required by law in Germany).
It is particularly advantageous here if the voltage generated by the voltage source has an amplitude between 0 and 1000 V, preferably 0 to 10 V, by particular preference 1 to 5 V. The current density at the outer surfaces of the doped diamond contact regions is here advantageously up to 10 A per cm2. 
The electrochemical cleaning, which takes place on instrument arms dipped in a liquid containing distilled water (here, if two arms of a pair of tweezers are dipped, the contact regions of the two arms are disposed at a fixed spacing from one another), is improved in that in addition the liquid is mixed with additives, such as solvents, cleaning agents, disinfectants, acids (e.g. sulphuric acid) and other, even solid/soluble additives or additives which cause the electrical conductivity. In addition, the liquid can also be heated or have ultrasound applied to it in order to accelerate or improve the cleaning effect.
A further advantageous embodiment of the instrument provides for the contact regions, e.g. on the respective arms of a pair of tweezers, to have the same or opposite polarity and in a corresponding manner be thus connected to the control unit or be responded to. Thus it is also possible, both during operation and in the subsequent electrochemical cleaning, to proceed optionally in a unipolar or bipolar manner; the polarity of the same instrument can be different during a coagulation operation and during a cleaning operation.